zxi dome size question

[turbodave]

other manufacturers of aftermarket heads for 1100 zxi's go no smaller than 31cc for use with 93 octane pump gas, yet your domes show 30cc for 91 octane. can you please explain why such a differance between your head and the others.

[Brooks]

The 1cc of volume equates to about 7lbs of cranking pressure. In the testing that we did, including dyno testing, we found the 30cc domes to work just fine with 91 octane fuel. The cranking pressure is around 160lbs at sea level.

[turbodave]

thanks, Brooks

[ss454trk]

And the maker of my head sez go no smaller than 33. and with the 33's i get 150 psi. Why does your head volume seem to have a lower cranking pressure than the other guys? What Horsepower difference would you see between the 32 domes and the 30s? Your head offers additional water ports? Your instructions don't say what to do with those ports. What should you do? Thanks

[Brooks]

If you have 33cc domes and you are getting 150 lbs at sea level, then that would be close to our readings. Our 32cc domes read around 150 at sea level. Then you have to consider that no two compression gauges will read the exact same. There is room for error in there. All of our domes are designed in AutoCAD and the volume is calculated from the 3d drawing. Then the cnc machine must be properly setup to cut the exact shape of the dome. All of our domes are cut the same, so it's all relative.

We didn't do any dyno testing with 32cc domes, as we were using 30cc dome with premium pump fuel. I doubt there would be a big difference however.

The additional water outlets are there for those that want and know how to run additional cooling or for custom pipe applications. We figured it was easier for us to provide the additonal holes than the have the customer drill the head themselves later. For instance, if you run dual cooling into the engine, then you would need to let more water out of the head.

[ss454trk]

Can you tell us the HP increase for 30cc over "stock"? I have heard that you should install an additional cooling outlet line for the front cylinder. Comment? And where would that line go? THanks for your response.

[Brooks]

If I remember correctly we gained 7 peak hp with the 30cc domes. It was a long time ago that we did the testing.

If you are going to run an additional line out of the front, you need to make sure that all 3 cylinders run at the same temperature. You should only need to run a line out of the front if the front cylinder is running hotter. You would just run it overboard to a bypass.

[ss454trk]

Thanks Brooks!!